High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.

We present the design parameters, production process, and in-flight performance of the X-ray telescope (XRT) onboard Suzaku. The imaging capability is significantly improved over the ASCA XRT, which had half-power diameters of ${3\rlap {.}{}^{\mathrm {\prime }}6}$, to ${1\rlap {.}{}^{\mathrm {\prime }}8}$–${2\rlap {.}{}^{\mathrm {\prime }}3}$ for all four XRT-I modules. The optical axes are found to be distributed within a radius of ${1\rlap {.}{}^{\mathrm {\prime }}3}$, which makes the observation efficiency of all the XRTs more than 97% at the XIS-default observing position. The vignetting over the XIS field of view predicted via ray-tracing coincides with that measured for observations of the Crab Nebula to within $\sim 10\%$. Contemporaneous fits of a power law to all of the XIS spectra of the Crab Nebula taken at the two standard observing positions (XIS/HXD-default positions) gives a flux consistent with that obtained by Toor and Seward (1974, AJ, 79, 995) to within $\sim 2\%$. The pre-collimator on the top of each XRT module successfully reduces the intensity of the stray light from the $20'$ and $50'$-off directions down to the level of pre-flight expectations.

Using ASCA data, we have measured the electron temperature in Abell 2163 out to 1.5 h −1 Mpc (3/4 of the virial radius, or 10a x , where a x is the X-ray core-radius) from the center, in three radial bins. The obtained temperatures are 12.2 +1.9 −1.2 keV, 11.5 +2.7 −2.9 keV and 3.8 +1.1 −0.9 keV in the 0-3 a x (0-3.5 ′ ), 3-6 a x and 6-13 a x spherical shells, respectively 5 . Formally applying the hydrostatic equilibrium and spherical symmetry assumptions and using these data together with the Ginga spectral and the Rosat imaging data, we were able to severely limit the possible binding mass distribution of the generic form ρ = ρ 0 (1 + r 2 /a 2 b ) −n/2 . All the allowed binding mass profiles are steeper than the gas density profiles and mass profiles with the same slope as gas are excluded at a greater than 99% confidence. The total mass inside 0.The strongest constraint on the mass profile is the observed quick drop of the temperature at large radii, which can only marginally be reconciled with the Rosat detection of gas at an even greater radius. We note that in the outer part of this cluster, which is likely to be a recent merger, the timescale for reaching electron-ion temperature equality via collisions is comparable to the merger timescale, so the measured electron temperature may give an underestimate of the gas pressure there. Otherwise, if our low value is indeed representative of the gas temperature in the outer shell, the cluster atmosphere should be convectionally unstable and gas turbulence should exist. Bulk motions of the gas are also expected during the merger. Their existense would increase the total gas pressure above that indicated by the observed temperature. Thus, failure of the model in which dark matter and gas have the same distribution at the radii of interest, which is favored by hydrodynamic simulations, may be due to the neglect of these phenomena, leading to an underestimate of the total density and overestimate of the baryonic fraction at large radii. The mass estimate at the smaller radius, where there is no evidence of departing from equilibrium, is likely to be correct.Our measured electron temperatures, combined with the previously reported Sunyaev-Zel'dovich decrement toward this cluster and the Rosat gas density profile, under the assumption of spherical symmetry, are consistent with a 5 Errors are 90% throughout the paper unless otherwise stated, and h ≡ H 0 /100 km s −1 Mpc −1 .-3 -Hubble constant between 42-110 km s −1 Mpc −1 (68% interval), where the uncertainty is dominated by that of the available SZ measurement.

The temperature and abundance structure in the intracluster medium (ICM) of the Hydra-A cluster of galaxies is studied with ASCA and ROSAT. The effect of the large extended outskirts in the point-spread function of the X-Ray Telescope on ASCA is included in this analysis. In the X-ray brightness profile, the strong central excess above a single β-model, identified in the Einstein and ROSAT data, is also found in the harder energy band (>4 keV). A simultaneous fit of five annular spectra taken with the GIS instrument shows a radial distribution of the temperature and metal abundance. A significant central enhancement in the abundance distribution is found, while the temperature profile suggests that the ICM is approximately isothermal with the temperature of ∼3.5 keV. The ROSAT PSPC spectrum in the central 1 ′ .5 region indicates a significantly lower temperature than the GIS result. A joint analysis of the GIS and PSPC data reveals that the spectra can be described by a two temperature model as well as by a cooling flow model. In both cases, the hot phase gas with the temperature of ∼3.5 keV occupies more than 90% of the total emission measure within 1 ′ .5 from the cluster center. The estimated mass of the cooler (0.5-0.7 keV) component is ∼2-6×10 9 M ⊙ , which is comparable to the mass of hot halos seen in non-cD ellipticals. The cooling flow model gives the mass deposition rate of 60 ± 30 M ⊙ yr −1 , an order of magnitude lower than the previous estimation.

Significant temperature variation is found from ASCA observations of the hot intracluster medium in the Coma cluster of galaxies. The whole cluster out to 1Њ from the center was covered by 14 pointings. The temperature of the hot gas in the outside region is estimated by correcting for the stray-light effect from the bright center. The inferred temperature is lower than 4.5 keV in the west region and higher than 10 keV in the east, both offset by 40Ј (1.6 Mpc for H 0 ϭ 50 km s Ϫ1 Mpc Ϫ1) from the center. The temperature variation is not explained by a systematic error in the complex point-spread function of the ASCA X-ray telescope. The azimuthal variation of temperature is probably caused by recent mergers and may reflect an extended distribution of the dark matter.